The incident at the South Fork at Ewing complex was quickly escalated to two alarms and prompted a response from rescue agencies in multiple surrounding towns and across the Delaware River.

John Sass, who lives on Willis Drive, in a neighborhood of single-family houses adjacent to the townhouse development, said he and his wife were having lunch at home about 12:20 p.m. when they heard the explosion. “We didn’t know if it was an air crash or something,” Sass said.

He closed all the windows, shut off the lights and went outside. “We saw the huge flames and you could see it billowing out,” he said.

Sass ran toward the fire, where he found three families with children who lived in the development and had left their homes. He brought them back to his house to stay warm. By 2 p.m. he said they had all left with family members.

Jamison Fort said he is still trying to find out the status of his home at 24 Crockett Lane. A police officer on the scene “couldn’t tell me for sure. The first two are definitely are gone, but they don’t know the extent of the damage.”

Fort was at work at Foundation Academy in Trenton when a fellow teacher told him about the explosion, so he headed home.

Ewing resident Flory Ferra said he came to the scene to check on a family member’s home. “Since my nephew lives back here, I took a ride over.” But his nephew got word to him that his house was not damaged.

Police had blocked off access to the development, but from the backyard of a nearby house, pieces of fiberglass insulation could be seen stuck in tree branches and scattered on the ground near the townhouses.

A school secretary at nearby Lore Elementary School on Westwood Drive, declining to give her name, said schools officials are responding to parents calling in about the fire, and students have not been sent home. Everyone at the school is “safe and fine at this time,” she said.

Multiple reports of burn injuries are being reported from the scene, though details were unavailable.

The Blood Council of New Jersey, which is based in Ewing, issued an emergency request for blood donations this afternoon due "to multiple injuries and an immediate need for blood" from local hospitals.

"We are directly supporting the hospitals and affected by the explosion," Anthony R. DeLuccio, spokesman for the Blood Council said. Visit www.GiveBloodNJ.org for more information.

A Vermeer D vertical driller, which is used for trench work, is visible from photos taken in the aftermath.

Richard Carroll, a nearby resident who was working from his Trenton office on South Broad Street, was looking out his window at the time of the explosion and saw large smoke clouds billowing into the sky, he said.

“I stopped at a friend’s house on Willis Drive that I was checking on between 1:30 and 1:45, and there was still a full fire going on,” he said. “Fire trucks were battling it, and police had the area cordoned off.”

At the time, Carroll said he did not see anyone injured at the scene.

“There was a lot of debris hundreds of feet from the explosion site, and I could see debris on adjacent houses,” Carroll said. “A lot of windows were blown out.”

Carroll said his friend felt the shockwave from the explosion all the way from Route 1 in West Windsor.